Trophic relations of decomposers on abandoned alpine pastureland

Earthworms are important macrodecomposers and engineers on alpine pastureland. They obviously affect decomposition and soil physical properties through digestion and bioturbation. However, there is little explicit recognition of the complexity of the processes which regulate the interactions of these soil invertebrates with microbes. These interactions determine the food palatability and food selection of these animals and finally the species composition and functional biodiversity.

To investigate the feeding ecology of the main decomposer species (earthworms and millipedes) on managed and abandoned alpine pastureland in the Central Alps three approaches will be followed up: In the proposed project

(1) we will reveal if the bacterial community in the invertebrate decomposer gut is, both in functional and structural sense, determined by the ingested food (litter type) or if it is species-specific,

(2) we will verify the trophic positions of the macrodecomposers by assessing stable isotope shifts between the saprotropic species and their diets and

(3) we will test if decomposer species preferentially feed on dwarf shrub litter in their natural habitats on abandoned pastureland as laboratory experiments have already suggested.

The rationale of this study is to improve the fundamental understanding of diversity-function relationships in decomposition processes under changing conditions at the alpine treeline. The linkage of soil zoological and microbiological approaches and the application of molecular techniques as well as the findings of the stable isotope shift experiment will promise important and innovative data on this subject.